A. Technical Field
The present invention relates to switching regulators, and more particularly, to systems, devices, and methods of calibrating single-phase and multi-phase programmable frequency DC-DC converters.
B. Background of the Invention
Modern devices, such as CPUs for notebooks, desktops, and the server market require regulated supply voltages and currents that satisfy stringent specifications with regard to stability, undershoot voltage, response time, and accuracy. CPU supply voltages are oftentimes provided by a single or multi-phase step-down voltage regulator with programmable switching frequency. Switching frequency and on-time are almost always set through an external circuit component (e.g., a resistor) of unknown value, which is connected to an unknown input voltage that serves as the supply of a switch mode power supply.
Constant on-time or constant off-time pseudo-constant frequency type buck converter architectures typically operate in current mode control and contain an internal slope compensation circuit intended to improve mainly two circuit characteristics: noise immunity and stability. These slope compensation circuits generate a voltage ramp having a fixed slope that is typically optimized only for a limited range of switching frequencies, typically at the center of the programmable operating switching frequency range of the of the buck converter. In the most trivial case, the ramp is generated by a current that charges a capacitor.
Since adjusting on-time or off-time with a circuit component to set the switching frequency does not affect the constant slope of prior art compensation circuits, existing buck converters may exhibit inconsistencies in stability, phase margin, and noise immunity, especially at the upper and lower boundaries of the available switching frequency range.
Fixed-frequency topologies with a variable on-time, but constant period typically require no slope adjustment. However, such designs do not provide a viable technical alternative to applications requiring a fast response time.